OS 15 FP help ???

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Air Scharnell
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OS 15 FP help ???

Post by Air Scharnell »

Picked up one of these old engines at a auction yesterday for $25
This thing is like NEW. Only missing part was the baffle section for muffler.

What AIR leaks should I be looking for on this older version???
Our carb problems with the needle valve?
draftman1
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Post by draftman1 »

I had wondered how those would work, the old Fp and max series. Parts would probably be getting tough to get. I wonder how much power they had? I have seen them go pretty cheap on ebay. but then what the heck, as long as it ran, and lasted a season or two, thats cheap running!
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lightning
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Post by lightning »

I've run a few FPs. They do not have quite the power of the OS15LA but they do have a stouter crank, six bolt head and a cast aluminum backplate. Had trouble getting them to hit over 17,000rpms, even with 30% fuel. Never had any air-leak problems with them.
Needles tend to break off the carb on impact but there is a remote conversion available to convert to carb to an inlet. Then almost any needle valve assy will work. (Including the original inserted in the fuel lines if you didn't break the carb end off yet!)
Don't worry about the muffler baffle - you don't need it. But it's the same muffler as the 15LA anyway.
Tower still has parts - I bought 15FP backplates for my LAs. (To get rid of that POS plastic version). They needed the flange skimming 20 thou to get the same crankcase penetration as the original part.
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Air Scharnell
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Post by Air Scharnell »

Thanks for the info Keith, I may have too use them for LSN 09
Since my Mags are turning 17k @ 5800 ft here.
sgilkey
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Post by sgilkey »

FPs are what we usually use for SSC. It's the rare FP that will exceed 17.5k at/near sea level (where we fly) on 10%, which I (as pit boy) like since I HATE fiddle farting with trying to detune an engine on race day. I remove the muff baffle, thread out the NVA so it is just peeking into the carb throat, and remove the head gasket. On 10-15% you'll I usually see about 17.2ish and that's just perfect for my tastes, you can get a bit more by juggling nitro and plug if you want to push the limit. Like Keith says, the front NV breaks off easily in a crash, which is frustrating, most of mine I have converted to RNV (OS sold this engine as RNV later in it's production run). The Tower 40 swept-back needle assembly is awesome for this engine and very damage-resistant, but I'm not sure if they still make it.... Overall I like the FP's user-friendliness and better NV compared to the Magnum XL, though I've run the Xl quite a bit and like it... Kirk Adams had excellent results using the magnum. Oh one other thing, the FP uses a 7/32 prop nut which is a kind of unusual size when you're looking for spinner nuts- it's the same as the TT GP15, Magnum GP15, etc. as compared to the 5mm on the LA, Mag XL/XLS.
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